Styling slot fallback content with ::slotted()

third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp

Index: third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
index 56922e0a2f1c887cff4b2ff2ad9603fc971d86d1..13f4c2f3843d5459ea9edfe30ed369ad25107b68 100644
--- a/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/ScopedStyleResolver.cpp
@@ -276,10 +276,13 @@ void ScopedStyleResolver::AddTreeBoundaryCrossingRules(
     CSSStyleSheet* parent_style_sheet,
     unsigned sheet_index) {
   bool is_document_scope = GetTreeScope().RootNode().IsDocumentNode();
+
+  // ::slotted() rules have to be allowed for Document for styling fallback
+  // contents in <slot>.
   if (author_rules.DeepCombinatorOrShadowPseudoRules().IsEmpty() &&
+      author_rules.SlottedPseudoElementRules().IsEmpty() &&
       (is_document_scope ||
-       (author_rules.ContentPseudoElementRules().IsEmpty() &&
-        author_rules.SlottedPseudoElementRules().IsEmpty())))
+       (author_rules.ContentPseudoElementRules().IsEmpty())))
     return;
 
   if (!author_rules.DeepCombinatorOrShadowPseudoRules().IsEmpty())
@@ -288,11 +291,10 @@ void ScopedStyleResolver::AddTreeBoundaryCrossingRules(
   RuleSet* rule_set_for_scope = RuleSet::Create();
   AddRules(rule_set_for_scope,
            author_rules.DeepCombinatorOrShadowPseudoRules());
+  AddRules(rule_set_for_scope, author_rules.SlottedPseudoElementRules());
 
-  if (!is_document_scope) {
+  if (!is_document_scope)
     AddRules(rule_set_for_scope, author_rules.ContentPseudoElementRules());
-    AddRules(rule_set_for_scope, author_rules.SlottedPseudoElementRules());
-  }
 
   if (!tree_boundary_crossing_rule_set_) {
     tree_boundary_crossing_rule_set_ = new CSSStyleSheetRuleSubSet();